Synthesis and characterization of water-soluble and bifunctional ZnO-Au nanocomposites

The ability to synthesize multicomponent nanocomposites (NCs) is important for exploring their functional properties of not only individual single components but also their combinations in technological applications. This paper presents an investigation on the synthesis and characterization of water-soluble and bifunctional ZnO-Au NCs, of which ZnO provides fluorescence and Au is used for organic functionality for bioconjugation. ZnO nanocrystals were employed as seeding material for nucleation and growth of reduced gold by citrate to form the water-soluble ZnO-Au NCs. The morphology and components of the ZnO-Au NCs, characterized by the TEM and XRD, respectively, demonstrate a dumbbell-like shape and crystalline wurtzite ZnO together with face-center-cubic Au nanoparticles. The surface plasmon absorption band of ZnO-Au NCs in aqueous solution is distinctly broadened and red-shifted relative to monometallic Au nanoparticles, and the UV emission intensity is higher by about I order of magnitude in ZnO-Au NCs than in pure ZnO nanocrystals; these observations reflect the strong interfacial interaction between ZnO and Au. Moreover, multiphonon Raman scattering of ZnO is also largely enhanced by the strongly localized electromagnetic field of the Au surface plasmon.